Research across both typically- and atypically-developing populations has suggested that difficulties regulating the autonomic nervous system (ANS) could contribute to impairments in social behavior. When the two branches of the ANS, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS), are working together successfully, it is theorized that a calm physiological state can be achieved that supports successful social responding. Individuals with autism spectrum disorder (ASD), a group typified by social impairments, have shown atypicalities in the functioning of both the PNS (e.g., lower cardiac vagal tone) and the SNS (e.g., higher arousal), as well as associations between ANS dysfunction and social difficulties. Based on our own recent work, we further posit that links between ANS dysfunction and atypical social development might relate to a broader set of sub-clinical characteristics that could be shared across individuals with ASD and their unaffected relatives. The present study will prospectively follow a group of infant siblings of children with ASD, a group with as high as a 1 in 5 chance of also developing the disorder (as compared to 1 in 68 in the general population) in order to look for early markers of atypical ANS activity that might be predictive of social difficulties. Infants at high risk for ASD (HRA) and low-risk controls (LRC; infants with no family history of ASD) will be followed from 6 to 18 months of age. Using eye-tracking and physiological recording methods, we will assess ANS functioning through pupil size, heart rate (HR), and skin conductance responses (SCR) at baseline and during emotional face processing tasks. Aspects of social and general functioning will also be evaluated through lab assessments and caregiver questionnaires. The major objectives of this work are to a) better understand differences in ANS functioning in HRA and LRC infants during the first year of life, and b) identify early atypicalities in ANS responses that might relate to concurrent and predictive measures of social behavior in both groups. This study is, to our knowledge, the first to focus on measures of both branches of the ANS (SNS and PNS) in HRA infants. This work has the potential to help in the identification of early markers of atypical social development, including symptoms relating to ASD, as well as broader characteristics that might also be found in unaffected relatives. Since early intervention is associated with more effective outcomes, improving early identification of developmental difficulties is essential for giving children the best chance of reaching their full potential. This project will expose College of Staten Island students to this broad public health goal and allow them to take active roles in conducting this methodologically-advanced and clinically-relevant study.